etween the different regions of
the globe is therefore regulated by the difference of geographical
position. The countries situated to the West are behind us; the Sun only
gets there after it has shone upon our meridian. When it is midday in
Paris, it is only 11.51 A.M. in London; 11.36 A.M. in Madrid; 11.14 A.M.
at Lisbon; 11.12 A.M. at Mogador; 7.06 A.M. at Quebec; 6.55 A.M. at New
York; 5.14 A.M. in Mexico; and so on. The countries situated to the East
are, on the contrary, ahead of us. When it is noon in Paris, it is
already 56 minutes after midday at Vienna; 1.25 P.M. at Athens; 2.21
P.M. at Moscow; 3.16 P.M. at Teheran; 4.42 P.M. at Bombay; and so on. We
are here speaking of real times, and not of the conventional times.

[Illustration: FIG. 60.--Motion of the Earth round the Sun.]

If we could make the tour of the world in twenty-four hours, starting
at midday from some place to go round the globe, and traveling westward
with the Sun, we should have him always over our heads. In traveling
round the world from West to East, one goes in front of the Sun, and
gains by one day; in taking the opposite direction, from East to West,
one loses a day.

In reality, the exact duration of the Earth's diurnal rotation is
twenty-three hours, fifty-six minutes, four seconds. That is the
sidereal day. But, while turning upon itself, the Earth circulates upon
its orbit, and at the end of a diurnal rotation it is still obliged to
turn during three minutes, fifty-six seconds in order to present exactly
the same meridian to the fixed Sun which, in consequence of the rotary
period of our planet, is a little behind. The solar day is thus one of
twenty-four hours. There are 366 rotations in the year.

And now let us come back to the consequences of the Earth's motion. In
the first place our planet does not turn vertically nor on its side, but
is tipped or inclined a certain quantity: 23 deg. 27'.

Now, throughout its annual journey round the Sun, the inclination
remains the same. That is what produces the seasons and climates. The
countries which have a larger circle to travel over in the hemisphere of
the solar illumination have the longer days, those which have a smaller
circle, shorter days. At the equator there is constantly, and all
through the year, a twelve-hour day, and a night of twelve hours.

[Illustration: FIG. 61.--Inclination of the Earth.]

In summer, the pole dips toward the Sun, and the rays of the orb of day
co